"I'm telling you right now, the United States left the WHO, and we're studying that, in the future. Either the WHO works without ideological bias, or we leave, too," the far-right leader told journalists.

Sometimes called a "Tropical Trump," Bolsonaro has followed a similar script to the US president in his handling of the pandemic, downplaying its severity, attacking state authorities' stay-at-home measures and touting the purported effects of hydroxychloroquine and a related anti-malarial drug, chloroquine, against COVID-19.

However, adding to the swirling scientific and political debate, a new study from Oxford University said Friday that hydroxychloroquine showed "no beneficial effect" in treating COVID-19.

In another potentially confusing reversal, the WHO changed its advice on face masks, saying that "in light of evolving evidence" they should be worn in places where the virus is widespread and physical distancing is difficult.